Although progress has been made on carbon nanotube (CN) based transistors in terms of both fabrication and understanding of their performance limits, challenges exist, for example, in process-compatible doping methods for CN field effect transistors (CNFET).
For many electronic devices there is a need for both p- and n-dopant. A positive-type or p-type semiconductor is obtained by carrying out a process of doping—adding a certain type of atoms to the semiconductor to increase the number of free charge carriers. Negative-type or n-type semiconductors include dopant atoms that are capable of providing extra conduction electrons to the host material.
In the case of carbon nanotubes and graphene, existing approaches include p-dopant which are stable in air and convert the nanotubes completely to p-doped materials. A p-CNFET can be converted to an ambipolar or n-CNFET via vacuum pumping. Although n-CNFETs can be formed by alkali metals or gas-phase doping, a controlled environment is required to prevent dopant desorption, because upon exposure to air, these devices quickly degrade and may become non-operational.
Accordingly, there is a need for an n-dopant that produces stable n-doped materials.